Iron deficiency is a common co-morbidity in heart failure, related with exercise intolerance, poor quality of life and unfavourable clinical outcomes (high all-casue and cardiovascular mortality and high rates of heart failure hospitalizations). Iron deficiency is diagnosed based on serum ferritin and transferrin saturation, but other biomarkers may be useful in the future (soluble transferrin receptor, hepcidin). Importantly, iron deficiency itself, relardless of haemoglobin level, has an unfavourable impact on symptoms and prognosis in patients with heart failure. Intravenous ferric carboxymaltose has been shown to improve clinical status in iron deficient symptomatic patients with stable heart failure and LVEF<45%. Ongoing clinical trials are investigating the impact of this therapy on morbidity and mortality in patients with acute and chronic heart failure.